186 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



As to the periodicity in various meteorological phenomena, " some 

 observations," writes Prof. Elias Loomis, " made in tropical countries, 

 indicate a periodicity in various meteorological phenomena, correspond- 

 ing to the changes of the solar spots, and some observations made 

 in the middle latitudes seem to point to like conclusions; but in order 

 to establish such a conclusion it is necessary to make a very extensive 

 comparison of observations, since the rain-fall at any one place is af- 

 fected by so many causes which we call accidental; that is, whose law is 

 not understood." 



The most extensive collection of observations of rain-fall in the United 

 States was made and published by the Smithsonian Institution in its 

 Contributions, No. 222, March, 1872. Mr. C. A. Schott has discussed those 

 observations with reference to periodicity (page 142), but does not ar- 

 rive at any positive result. 



From a later publication ^^ we make the following extracts: 



The character of the secular variation in the mean annual temperature, as exhibited 

 on the accompanying plate, is that of a series of irregular waves representing a suc- 

 cession of warmer and colder periods, during which, however, the mean temperature 

 deviates only about one or two degrees, in excess or defect, from its normal value. Ir- 

 respective of minor irregularities, which have to some extent been eliminated, some of 

 the single progressions appear quite systematic ; thus, for instance, at New Haven, the 

 temperature steadily declined from 1802 to 1817, it then iucreased till 1827, after which 

 it again decreased, reaching a decided minimum in 1836. These uudulations, when 

 compared for a number of stations exposed to similar climatological conditions, ap- 

 proach to parallelism over large tracts of country, and exhibit considerable uniformity 

 in their general character. — (Page 310.) 



Thus from Maine to Georgia these waves are of a broad and well-defined shape, as at 

 New Haven ; but they become somewhat changed in their appearance over the vast 

 area watered by the Mississippi and its tributaries. Here the modulations become 

 more narrow and numerous, as at Fort Snelliug. * * * On our west coast, as might 

 have been expected, a new feature is developed, subject, perhaps, to less irregularities 

 than in any other part of the country. * * * 



The degree of parallelism of the curves is sufficiently close to warrant an additional 

 consolidation of results for a few characteristic stations, for further study ; one typical 

 curve will be given for the Atlantic coast, and another for the Mississippi Valley. 



The first is composed of the long series of mean annual temperatures at Brunswick, 

 Me. ; Salem, Mass. ; New Haven, Conn, ; and Philadelphia, Pa., to represent during 

 ninety-one years the type of the secular change for those Eastern States which are 

 situated between the Atlantic and the Alleghany Mountains. * * * (Pjige 311.) 



The second type curve is made up from the stations : Fort Suelling, Minn. ; Muscat- 

 tine, Iowa; Fort Leavenworth, Kans. ; and Fort Gibson, Ind.T. * « * (i^age 313.) 



The distinguishing features * * * of these two type curves appear well marked. 

 The longer waves of the Atlantic stations show : Principal maxima in 1802, 1826, 1846, 

 1865, and principal minima in 1785, 1816, 1836, 1857 ; the average interval being about 

 twenty-two years. The shorter waves of the interior States show : Principal maxima 

 in 1827, 1833, 1839, 1845, 1854, 1860, and principal minima in 1831, 183G, 1843, 1848, 1856, 

 1867 ; the average interval l3eing about seven years. These undulations, however, are 

 not sufficiently regular or sufficiently distinct, being mixed with subordinate fluctua- 

 tions, to serve as a basis of prediction ; all that can be claimed for them is a general 

 exponent of the character of the secular change. — (Page 314.) 



For the purposes of comparison and study we give also the following 

 tables of meteorological data, for which we are indebted to the Chief 

 Signal Officer of the Army, and which relate to the recent years, for 

 which we have also abundant information as to the locust invasions: 



25Tables, Distribation, and Variation of the Attaospheric Temperature in the United States. * * * 

 By Charles A. Schott. Smithsonian Contributions to Knowledge, Vol. XXI, Ko. 277, 1876. 



